Left brain stands guard while sleeping away from home

In unfamiliar surroundings, part of the left hemisphere keeps watch while the rest of the brain is deeply asleep, scientists report April 21 in Current Biology. The results help explain why the first night in a hotel isn’t always restful.

Some aquatic mammals and birds sleep with half a brain at a time, a trick called unihemispheric sleep. Scientists have believed that humans, however, did not show any such asymmetry in their slumber.

Study coauthor Yuka Sasaki of Brown University in Providence, R.I., and colleagues looked for signs of asymmetry on the first night that young, healthy people came into their sleep lab. Usually, scientists toss the data from the inaugural night because the sleep is so disturbed, Sasaki says. But she and her team thought that some interesting sleep patterns might lurk within that fitful sleep. “It was a little bit of a crazy hunch,” she says, “but we did it anyway.”